The role of dyadic interactions in the mixed-mating strategies of the mangrove rivulus Kryptolebias marmoratus

The mangrove rivulus Kryptolebias marmoratus a small cyprinodont fish native to tropical and subtropical waters from Florida to Brazil, is one of two known self-fertilizing, hermaphroditic vertebrates of which K. marmoratus displays androdioecy, a complex system of reproduction in which hermaphrodites and males are present. This study describes the behavioral repertoires observed during dyadic interactions in the laboratory. Kryptolebias marmoratus exhibited 23 distinctive acts or behaviors. Acts were divided into four categories: aggressive, submissive, neutral, and reproductive. Leading and following behaviors played important roles in the behavioral repertoires of these fish. In hermaphrodite-male dyads, males exclusively initiated the reproductive process and actively pursued hermaphrodites. When hermaphrodites were paired, there was no evidence that they behaved like other simultaneous hermaphrodites that alternate sexual roles (e.g. serranids). Hermaphrodites were extremely aggressive towards one another, and the aggressor established dominance rapidly. Male-male dyads were divided into two subdivisions based on the presence or absence of the caudal ocellus on one fish. A caudal ocellus on one male appeared to signal the possibility of a potential mating partner to males lacking it. Pairings of males without an ocellus were similar to hermaphrodite-hermaphrodite dyads in that both members of the pair were aggressive towards one another. These observations may be indicative of interactions taking place in natural communities or assemblages of fish in which both males and hermaphrodites occur and provide evidence on the role of dyadic interactions in the mixed-mating strategies [Current Zoology 56 (1): 6-17, 2010].     

Size-dependent Mating Behaviours of Male Sand-bubbler Crab,Scopimera globosa: Alternative Tactics in the Life History

Factors leading to the separation of mating behaviours were investigated in the sand-bubbler crab, Scopimera globosa. The crabs mated on the surface (surface copulation, SC) and underground (UC). UC males were large (old) whilst SC males were small (young). Burrowless females bred in the UC males' burrows. These females accepted UC in exchange for access to a burrow. UC occurred much more frequently than SC in the burrow area in which females oviposited. Most SC occurred in the water-saturated area affording a rich diet. SC was accepted by most large and small females in both areas and most UC by small females in the burrow area. SC was an alternative to UC for males in that there was a size dependence between types of copulation. These two mating behaviours involved different degrees of interaction with neighbouring males. Males attempting to carry a female to their burrows for UC were more often disturbed by other males than were males attempting SC. In the interaction for both UC and SC, larger males were likely to resist the disturbances. UC males needed their own burrows, but these burrows were not enlarged before mating. UC males have a higher paternity of eggs than SC males, because SC males' sperm is often displaced by other males. Thus, UC was a behaviour with relatively higher costs and benefits for male crabs than SC behaviour. Alternative mating behaviours in male S. globosa are conditional, and explained by intrasexual interactions and a male life history strategy with a trade-off between growth and reproduction. It is not likely that the size dependence of male mating behaviour is caused by mate preference of females for UC males in the burrow area.     

Microsatellite documentation of male-mediated outcrossing between inbred laboratory strains of the self-fertilizing mangrove killifish (Kryptolebias Marmoratus)

Primers for 36 microsatellite loci were developed and employed to characterize genetic stocks and detect possible outcrossing between highly inbred laboratory strains of the self-fertilizing mangrove killifish, Kryptolebias marmoratus. From attempted crosses involving hermaphrodites from particular geographic strains and gonochoristic males from others, 2 among a total of 32 surveyed progenies (6.2%) displayed multilocus heterozygosity clearly indicative of interstrain gametic syngamy. One of these outcross hybrids was allowed to resume self-fertilization, and microsatellite assays of progeny showed that heterozygosity decreased by approximately 50% after one generation, as expected. Although populations of K. marmoratus consist mostly of synchronous hermaphrodites with efficient mechanisms of internal self-fertilization, these laboratory findings experimentally confirm that conspecific males can mediate occasional outcross events and that this process can release extensive genic heterozygosity.     

BEST OF BOTH WORLDS? ASSOCIATION BETWEEN OUTCROSSING AND PARASITE LOADS IN A SELFING FISH

Mixed-mating strategies (i.e., intermediate levels of self-fertilization and outcrossing in hermaphrodites) are relatively common in plants and animals, but why self-fertilization (selfing) rates vary so much in nature has proved difficult to explain. We tested the hypothesis that parasites help maintain mixed-mating using a partially selfing fish (Kryptolebias marmoratus) as a model. We show that outcrossed progeny in the wild are genetically more diverse and less susceptible to multiple parasite infections than their selfed counterparts. Given that outcrossing in K. marmoratus can only be attained by male-hermaphrodite matings, our data provide an explanation for the coexistence of males and hermaphrodites in androdioecious species where hermaphrodites are unable to outcross among themselves. Moreover, our study provides evidence that parasites contribute to maintaining mixed-mating in a natural animal population.     

Epigenetic regulation of sex ratios may explain natural variation in self-fertilization rates

Self-fertilization (selfing) favours reproductive success when mate availability is low, but renders populations more vulnerable to environmental change by reducing genetic variability. A mixed-breeding strategy (alternating selfing and outcrossing) may allow species to balance these needs, but requires a system for regulating sexual identity. We explored the role of DNA methylation as a regulatory system for sex-ratio modulation in the mixed-mating fish Kryptolebias marmoratus. We found a significant interaction between sexual identity (male or hermaphrodite), temperature and methylation patterns when two selfing lines were exposed to different temperatures during development. We also identified several genes differentially methylated in males and hermaphrodites that represent candidates for the temperature-mediated sex regulation in K. marmoratus. We conclude that an epigenetic mechanism regulated by temperature modulates sexual identity in this selfing species, providing a potentially widespread mechanism by which environmental change may influence selfing rates. We also suggest that K. marmoratus, with naturally inbred populations, represents a good vertebrate model for epigenetic studies.     

A Sexually Conditioned Switch of Chemosensory Behavior in C. elegans

In sexually reproducing animals, mating is essential for transmitting genetic information to the next generation and therefore animals have evolved mechanisms for optimizing the chance of successful mate location. In the soil nematode C. elegans, males approach hermaphrodites via the ascaroside pheromones, recognize hermaphrodites when their tails contact the hermaphrodites'' body, and eventually mate with them. These processes are mediated by sensory signals specialized for sexual communication, but other mechanisms may also be used to optimize mate location. Here we describe associative learning whereby males use sodium chloride as a cue for hermaphrodite location. Both males and hermaphrodites normally avoid sodium chloride after associative conditioning with salt and starvation. However, we found that males become attracted to sodium chloride after conditioning with salt and starvation if hermaphrodites are present during conditioning. For this conditioning, which we call sexual conditioning, hermaphrodites are detected by males through pheromonal signaling and additional cue(s). Sex transformation experiments suggest that neuronal sex of males is essential for sexual conditioning. Altogether, these results suggest that C. elegans males integrate environmental, internal and social signals to determine the optimal strategy for mate location.     

Behavioural evidence for body colour signaling in the fiddler crab Uca perplexa (Brachyura: Ocypodidae)

In the reproductive season, mature females of the fiddler crab Uca perplexa leave their burrows and wander about their habitat for mating. To clarify whether the fiddler crabs respond to colour or luminosity, I examined the behavioural responses of the males to the wandering females before and after the females were painted white, red, black or blue. The behaviours of the males were categorized into three types: lateral–circular wave and lateral–straight wave for courting, and repelling. Before painting, almost all of the males courted the females. After painting, significantly fewer males courted the red-, black- and blue-painted females than courted the white-painted females. These results mean that the fiddler crabs can discriminate colours or luminosity. The role of body colour as a visual signal in crab society is discussed.     

Testing the role of male–male competition in the evolution of sexual dimorphism: a comparison between two species of porcelain crabs

Theory predicts marked sexual dimorphism in terms of body size and body structures used as weapons (e.g. chelipeds) in gonochoric species with intense male sexual competition for receptive females and reduced or no sexual dimorphism in species where competition among males is trivial. We tested this hypothesis using a pair of closely‐related species of symbiotic porcelain crabs as a model. In one species that inhabits sea anemones solitarily, competition among males for receptive females is unimportant. In a second species that dwells as dense aggregations on sea urchins, male–male competition for sexual partners is recurrent. We expected considerable sexual dimorphism in body size and weaponry in the urchin‐dwelling crab and reduced sexual dimorphism in the anemone‐dwelling crab. In agreement with expectations, in the urchin‐dwelling crab, male body size was, on average, larger than that of females and males invested considerably more to cheliped length than females. Also supporting theoretical considerations, in the anemone‐dwelling crab, sexual dimorphism in terms of body size was not detected and differences between the sexes in investment to cheliped length were minor. Interestingly, chelipeds were more developed both in males and females of the anemone‐dwelling crab than in the urchin‐dwelling crab as a result of the importance of these structures for monopolization of their naturally scarce anemone hosts. Another difference between the studied species was the existence of two clearly distinguishable ontogenetic phases in males of the urchin‐dwelling crab but not in males of the anemone‐dwelling crab. Whether the two different male morphs display different male reproductive strategies in the urchin‐dwelling crab remains to be addressed. Other conditions that might additionally explain the observed differences in sexual dimorphism (e.g. female mate choice) between the studied species remain to be explored. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 548–558.     

Female sexual behavior displayed by androgenized female rhesus macaques

Adult, prenatally androgenized female rhesus macaques (female pseudohermaphrodites) that had been ovariectomized were treated with estradiol benzoate (20 micrograms/day) and paired with males at weekly intervals for 4 weeks beginning on Day 12 of injection. Their sexual behavior was compared to that of a control group of females. The sexual behavior of the males toward the two groups of genetic females (control females with normal female genitalia and hermaphrodites with well-formed male genitalia) was also observed. Females and hermaphrodites were equally receptive to male invitations to copulate. Although there were some differences in the specific components of proceptive behavior displayed by the two groups, the overall differences were negligible. Earlier studies had shown that infant and juvenile hermaphrodites resemble males in patterns of play and sexual behavior. When treated with testosterone as adults and paired with receptive females, they displayed mounting patterns typical of males--one of seven hermaphrodites achieved intromission and ejaculated. It has now been demonstrated that when treated with estrogen and paired with males, they responded as females. Hence, the capacity to behave sexually as males is not incompatible with the capacity to respond sexually as females under certain hormonal and environmental conditions.     

A preference for a sexual signal keeps females safe

Predation is generally thought to constrain sexual selection by female choice and limit the evolution of conspicuous sexual signals. Under high predation risk, females usually become less choosy, because they reduce their exposure to their predators by reducing the extent of their mate searching. However, predation need not weaken sexual selection if, under high predation risk, females exhibit stronger preferences for males that use conspicuous signals that help females avoid their predators. We tested this prediction in the fiddler crab Uca terpsichores by increasing females' perceived predation risk from crab-eating birds and measuring the attractiveness of a courtship signal that females use to find mates. The sexual signal is an arching mound of sand that males build at the openings of their burrows to which they attract females for mating. We found that the greater the risk, the more attractive were males with those structures. The benefits of mate preferences for sexual signals are usually thought to be linked to males' reproductive contributions to females or their young. Our study provides the first evidence that a female preference for a sexual signal can yield direct survival benefits by keeping females safe as they search for mates.     

Abundant males in populations of a selfing hermaphrodite fish, Rivulus marmoratus, from some Belize cays

The killifish Rivulus marmoratus is the only known selfing hermaphroditic vertebrate, and males of the species are usually exceedingly rare or non-existent in nature. Collections on several Belize cays in 1988 and 1989 yielded 13.5–24% males. Factors responsible for this unusually high proportion of males are currently not understood. Likewise, the biological significance of males in populations which otherwise consist of selfing hermaphrodites (with internal fertilization) is problematic and awaits further study.     

Sex determination in the androdioecious barnacle Scalpellum scalpellum (Crustacea: Cirripedia)

How androdioecy (coexistence of hermaphrodites and males) is maintained is still poorly understood. Therefore, sex determination was studied in the androdioecious barnacle Scalpellum scalpellum L. First, 247 cypris larvae from seven broods were investigated for sexual dimorphism in larval morphology and found to be all identical. Second, experiments with cyprids showed that males and hermaphrodites differ distinctly in morphology as soon as 4–5 days after settlement. Third, 14 252 cyprids were allowed to settle on the bottom of their culture cages, and all surviving larvae developed into hermaphrodites and none into dwarf males. Fourth, larvae settled in hermaphrodite receptacles (i.e. future males) were removed at increasing intervals after settlement to study if the male and hermaphrodite sexual expressions are fixed or plastic. All larvae became dwarf males if allowed to stay there for more than 8 h after settlement. But if removed within 3 h after settlement, half of them developed into hermaphrodites. We conclude that an environmental sex determination mechanism operates in S. scalpellum. Together with a 1:1 hermaphrodite/male ratio observed in previously reported experiments offering a free choice of settlement, we suggest that all larvae are potential hermaphrodites, but only 50% can settle in hermaphrodite receptacles and yield males.     

Managing the invasive crayfish Procambarus clarkii: Is manual sterilisation the solution?

1. Management of invasive alien crayfish is challenging, as once established their eradication or control is difficult, even impossible in some areas. Sterile male release technique has been previously assessed in crayfish with encouraging results, however, the methods have not demonstrated the complete sterility of released competitive males. The present study explores whether manual removal of male gonopods, i.e. the appendages responsible for sperm transfer, as a sterilisation technique, might affect male competitiveness and sexual behaviour as well as reproductive potential in the red swamp crayfish Procambarus clarkii.
2. Under controlled laboratory conditions, we analysed the agonistic and sexual behaviour of 64 treated and 64 control males both coupled with a female in single pairs, and 40 treated and 40 control males together with 80 females in a natural-like social context.
3. Removal of gonopods partly altered sexual behaviour, affecting duration of copulation and competitiveness in treated males. However, male readiness to initiate sexual interaction with females was not affected by the treatment. Treated males needed to invest more in agonistic interactions with females to successfully dominate a female for the copulation to take place. Females coupled with treated males did not produce any offspring, compared to females coupled with control males. Treated males were able to regenerate removed gonopods, even if sometimes only partially or malformed. Females that mated with 11 treated males with regenerated gonopods did not produce any juveniles.
4. Although treated males managed to mate with females and impair their reproductive capability under the laboratory conditions, shorter copulation and elevated number of abdominal extensions were observed in treated couples. This indicates that males and/or females are able to sense the lack of gonopods and/or lack of the contact. We believe that female receptivity after an initial mating requires further investigation. Assessment of receptivity in an experimental setting where females are provided with refuges (e.g. burrows) would help us to elucidate whether there is a compensation for unsuccessful copulation. More research is needed on underlying biological mechanisms to better assess male competitiveness, technique effectiveness and limits of technique application.

     

Implications for the Maintenance of Androdioecy in the Freshwater Shrimp, Eulimnadia texana Packard: Encounters between Males and Hermaphrodites are not Random

Androdioecy is a mixed‐mating system in which there are males and hermaphrodites but no pure females. Few species exhibit such a mating system. Eulimnadia texana is a branchiopod crustacean that has recently been identified as an androdioecious species. This system is ideal for testing questions related to the evolution of sexual reproduction. We are testing a model that predicts androdioecy to be a stable mixed‐mating system under certain conditions. Specifically, we investigated whether encounters between males and hermaphrodites are random or if either sex seeks out the other for mating. Focal male or hermaphrodite clam shrimp were presented with stimulus shrimp of the other sex or kept alone. Swimming speed and time spent within different areas of a test chamber were recorded. Males did not alter mean swimming speed or spend more time than expected by chance near partitioned hermaphrodites. Hermaphrodites, however, decreased mean swimming speed in the presence of males and also spent more time than expected by chance near partitioned males, suggesting that hermaphrodites respond to male chemical and/or visual stimuli. Modified swimming behaviour probably facilitates inter‐sexual contact, thereby increasing opportunities for out‐crossing above that expected by random encounters.     

Protandric simultaneous hermaphroditism in the shrimps Lysmata bahia and Lysmata intermedia

Abstract. The sexual system of two peppermint shrimps, Lysmata bahia and Lysmata intermedia, inhabiting intertidal fossil coral terraces at Bocas del Toro, on the Caribbean coast of Panama, was examined. Dissections suggested that the population of each species consisted of functional males and functional simultaneous hermaphrodites. Males have cincinulli and appendices masculinae on the first and second pair of pleopods, respectively, gonopores located at the coxae of the third pair of walking legs, and ovotestes with a well‐developed male portion full of sperm, but an undeveloped female portion. Hermaphrodites lacked appendices masculinae and cincinulli. However, they have male gonopores and ovotestes with well‐developed ovaries full of mature oocytes and testes with sperm. When hermaphrodites were maintained in pairs, both molted and spawned eggs (to beneath abdomen) that continued developing after 3 d, demonstrating that hermaphrodites can reproduce as males and inseminate other hermaphrodites acting as females. The possibility of self‐fertilization or parthenogenetic reproduction was tested and disregarded, because hermaphrodites reared in isolation spawned oocytes that failed to develop, disappearing from the abdomen after 2 d. Males reared in pairs mature as hermaphrodites in <50 d, showing the ability of males to mature as hermaphrodites. These results demonstrate that L. bahia and L. intermedia are protandric simultaneous hermaphrodites, as reported for all species of this genus whose sexual system has been examined. However, the studied species featured a lifestyle, termed “tropical‐low abundance,” here not recognized previously for the genus; they occur in low abundances in tropical environments, they do not develop symbiotic associations with sessile invertebrates, and they are not conspicuously colored. Information on the sexual systems and lifestyles of more species needs to be examined before these observations can be placed into a comparative context within the genus.     

Development of social behaviour in chickens: A factor analysis

Factor analysis was used to describe the week by week changes in the frequency of a wide range of behaviours of chickens. Oblique rotation resulting in correlated factors was compared with the more conventional orthogonal rotation, and was found to provide a clearer interpretation of the factors. Mixed sex groups of chickens were observed from hatching until sexual maturity, and the changes in the occurrence of agonistic behaviours could be described in terms of three factors. Factor 1 involved early sparring and running, but there was some doubt as to whether this should be labelled aggressive. Factor 2 involved non-reciprocated leaping, horizontal neck threats, and headpecks between males. Factor 3 involved threats and headpecks between males and females. Sexual development could be described by two factors; the first involving sexual development of the male, and the second the beginning of sexual interactions between males and females. Waltzes and rear approaches were associated with the sexual development of males, while chases were associated with sexual interactions. There was an increase in the frequency of prolonged male—male agonistic encounters when these sexual interactions began to occur.